This invention involves an improvement in well service valves for injection of treating fluid into low pressure formations. More specifically, this invention provides an improved well treating valve having a partial pressure-balancing system. There are several known treating valves utilizing the spring loaded checkvalve principle to inject fluids in precontrolled amounts into low pressure formations. Examples of one type of such valve are disclosed in the Burt reissue Pat. No. RE 22483, the Watson U.S. Pat. No. 3,802,507, and in the 1964-65 World Oil Composite Catalog, pages 3680 and 3681. All of the above mentioned devices utilize a coil spring biasing means on a checkvalve member to provide wall injection valve systems. The basic disadvantage with these devices is that the biasing means utilized must be of sufficient strength to provide a biasing force exceeding the hydrostatic pressure in the tubing due to the column of fluid above the valve.
In some of the deeper wells, this results in utilizing a very stiff biasing spring to obtain proper operation of the injection valve. Because of this requirement, the valve usually operates only a few times successfully because of weakening or breaking of the stiff valve spring. The present invention overcomes these disadvantages by providing an injection valve having a partial pressure-balancing feature which eliminates the need for a heavy biasing spring since the high hydrostatic pressure head above the valve in the tubing is substantially offset by the partial pressure-balancing feature. The present invention allows the use of a weaker, more resilient biasing means such as a coil spring.